iMovie '09 Not Responding During Export

I am having issues exporting movies of all sizes using iMovie. Upon exporting, the time for completion initially says about 5 minutes and then increases to about an hour before the application says it's not responding and the spinning wheel of death appears. When this happens, it maybe makes some progress but it's hard to tell. This occurs even when trying to export tiny movies.

The movie in question is 3 minutes long and includes about 80 quick clips. An mp3 is used for a soundtrack. The footage was taken with a Nikon D5100 and D7000 at 1080p/24fps, and it is stored on the local hard drive. I'm using an iMac with 4g of RAM and a 3.06 GHz Intel Core Duo processor, and it's running Lion.

To combat the problem, I've restarted my computer, closed all other applications, repaired disk permissions and verified the disk, which came back without problems.

Am I just being impatient with the exporting time and is the unresponsiveness normal at times or is there something else going on that I can fix?